Did Japan Have a Secret Plan to Arm It's Aircraft Carrier with F-35s?

Very nearly since the day Japan laid down JS Izumo (and her sister, Kaga) analysts have wondered whether the medium-sized aircraft carrier might eventually fly the F-35B Joint Strike Fighter (JSF). At 27,000 tons and 814 feet long, the Izumos are clearly large enough to operate the F-35B, the short take-off and vertical landing aircraft (STOVL) variant of JSF family. Moreover, Japan has recently expressed interest in acquiring a number of F-35Bs, officially for the purpose of operating from landing strips on small islands near the East China Sea.

Now, a source is reporting that the Izumo was in fact designed with the F-35B in mind. The Japanese Ministry of Defense has denied plans to retrofit Izumos to carry the fighter (they currently only carry helicopters), but Asahi Shimbun has reported that Izumos were, in fact, designed to carry the F-35B. Designating the ships “helicopter destroyers” is a way of avoiding controversy, domestic and international, over Japan’s possession of potentially offensive naval aviation capabilities.

As international subterfuge goes, this is really a mild case. But it’s hardly the first time that Japan has engaged in a bit of sleight-of-hand with respect to its carrier force. Prior to World War II, operating on limited funds and under the restrictions of the Washington Naval Treaty, the Imperial Japanese Navy (IJN) facilitated the construction of numerous ships designed for conversion into aircraft carriers. Many of these ships went on to play large roles in the campaigns of the Pacific War, although most were lost in the conflict.

Ryuho

The Washington Naval Treaty did not limit the construction of such supplementary vessels in the way that it limited carrier construction. But the IJN realized that it would need carriers more than it would need seaplane or submarine tenders. Accordingly, it designed numerous auxiliary ships with conversion in mind, the idea being to evade the terms of the treaty.

The first surreptitious conversion was HIJMS Taigei. Constructed between 1933 and 1934, she served as a submarine tender during the Sino-Japanese War. Three days before Pearl Harbor, she was ordered to return to Yokosuka to begin conversion to an aircraft carrier. Ryuho (she acquired a new name during the process) re-entered service in November 1942. The results weren’t ideal; her hull strength and engine reliability were both low. She displaced 16,500 tons, but could only carry thirty-one aircraft. Ryuho was generally kept away from major combat operations, although she did participate in the Battle of Philippine Sea. She survived the war, although an air attack in March 1945 left her a burned out hulk.

Shoho and Zuiho

The IJN performed the same trick with Shoho and Zuiho, which began life as Tsurugizaki and Takasaki, another pair of submarine tenders. Only the former was completed in her original role, however. As aircraft carriers they were fast and useful, each displacing 11500 tons, and carrying thirty aircraft. Shoho was destroyed by American carrier aircraft at the Battle of Coral Sea; Zuiho, having served in most of the major engagements of the Pacific War, was sunk at the Battle of Leyte Gulf in 1944.

Chitose and Chiyoda

Around the same time as HIJMS Taigei, the IJN ordered a pair of seaplane carriers named Chitose and Chiyoda, with similar convertible characteristics. When the scarcity of carriers became clear during the Guadalcanal campaign, both ships underwent reconstruction. As carriers, Chitose and Chiyoda displaced 11,500 tons, and could each carry thirty aircraft. Both ships were destroyed by William Halsey’s 3rd Fleet at the Battle of Leyte Gulf, sacrificed as part of a diversionary operation.